Temper-ESP8266

Temper is a compact, low power temperature sensor based on ESP8266 and SHT30 with large 13x7 pixel led display.

Low power, only consumes ~30-40uA while asleep. With 400mA battery it should last months on single charge.
SHT30 provides very accurate, factory calibrated measurement capability.
Super simple Web config (see screenshot here)
Home Assistant compatible including auto-discovery, but can be used with any other platform supporting MQTT.
13x7 pixel led display
TP4054 charging IC onboard for easy charging via USB
Can be attached to a wall using magnets (see thingiverse for details).

How does this thing work?

After it's set up in config portal, it periodically wakes up and publishes Temperature, Humidity and Battery percentage through MQTT
Pushing the reset button will force send current data and show Temperature on the display

Hot air station / reflow oven (SHT30 has pins at the bottom, can't be hand-soldered)
Components listed in "PCB and BOM" directory (lcsc and aliexpress links provided)
Plastic case (download on thingiverse)
Hot glue to fixate pcb in the enclosure
Patience
You can order it with most of the components pre-assembled from JLCPCB (you can find Pick&Place + BOM + Gerber in the above mentioned directory). Partially assambled pcbs will cost you little over $60 for 10pcs, see components information in "PCB and BOM" directory.